The present invention relates to a method of producing vinyl chloride resin compositions having excellent impact resistance and simultaneously satisfying requirements for weather resistance as well as processability.
More particularly, the present invention is concerned with resin compositions comprising vinyl chloride resins with multicomponent resins incorporated therein, said multicomponent resin being prepared by graft polymerizing acrylonitrile, a vinyl monomer essentially containing alkyl methacrylates and a cross-linking agent onto a cross-linked copolymer rubber obtained by emulsion-polymerizing an alkyl acrylate and butadiene in the presence of a cross-linking agent or onto a cross-linked terpolymer rubber obtained by emulsion-polymerizing an alkyl acrylate, butadiene, and methyl methacrylate in the presence of a cross-linking agent under specific conditions.
A great number of attempts have been heretofore made to improve the impact strength of vinyl chloride resins. Especially, an impact-resistance-improving resin obtained by graft polymerizing styrene and methylmethacrylate or styrene and acrylonitrile onto a butadiene-based rubber, which is hereinafter referred to as ABS resin, has excellent properties and has been widely used. However, a vinly chloride resin containing such ABS resin mixed therein has poor weather resistance and, therefore, cannot be used outdoors.
That is, the ABS-modified vinyl chloride resin truely possesses high impact resistance immediately after it is moulded, but it is observed that, when it is once used in the outdoors, it cannot maintain such a high impact strength, and its strength is rapidly reduced. For this reason, such resins are greatly limited in their use as construction materials.
The reduction in strength is considered primarily due to the ultraviolet degradation of the butadiene component contained in the ABS resin. On the basis of this consideration, attempts have been made to develop a reinforcing agent comprising rubber components excellent in weather resistance other than butadiene-based rubber components. Among them, representative reinforcing agents include copolymer rubbers of ethylene and vinyl acetate onto which vinyl chloride is graftpolymerized, acrylate-based rubbers onto, which monomers such as styrene, methylmethacrylate, acrylonitrile, etc. are graftpolymerized, and the like.
However, some of these agents impair the mechanical properties of vinyl chloride resin compositions relating to such as tensile strength, softening temperature, to a remarkable extent, while others are unable to impart sufficient strength to the vinyl chloride resin. Further, a great disadvantage common to these reinforcing agents in that the impact strength of vinyl chloride resin compositions containing these reinforcing agents vary to a much greater extent depending upon the processing conditions under which these compositions are processed as compared with the vinyl chloride resin compositions containing ABS resin. That is, some of these resin compositions certainly have an appreciable impact strength under suitable moulding and processing conditions, but these resin compositions, in general, have the disadvantage of their impact strengths being greatly varied with change in these conditions (for example, the degree of kneading).
The degree of kneading during the moulding and processing of the vinyl chloride resin changes to a remarkable extent depending upon the type and operation conditions of the moulding machine and the type and amount of processing aids added in the process. It is thus undesirable for practical purpose that the impact strength of the moulded articles be remarkably reduced according to the change of the degree of kneading. In order to overcome this disadvantage, there have been proposed various methods such as, for example, a method comprising pre-treating a rubber component with a peroxide before graft polymerizing a grafting component thereonto so as to form active sites for graft polymerization or a method comprising using a copolymer of butadiene and an alkyl acrylate containing larger proportion of butadiene. However, the former is still unsatisfactory in imparting strength, while the latter entails the problem of weather resistance.